Sharpness in context

[thombrogan]

Many of us have had the pleasure of having a knife which couldn't shave arm hair nonetheless perform whatever boxcutting, woodchopping, or food prep needs we assigned to said knife. We've also had the disappointment of having a knife sharp enough to whittle hairs, but become a triceps and forearm exercise while cutting.

Swaim, Johnston, Stamp, Talmadge, et al have explained this apparent dichotomy to be a case of sharpness versus cutting ability. Some of the listed authors; especially the ever-prolific et al; have even taken measurements of exerted force as demonstration. I believe their work was and will continue to be of great importance, but I also believe the dichotomy between sharpness and cutting ability resolves when sharpness is measured in the context of what's being cut and how it's being cut.

Of course, one can have a blisteringly keen edge which not only whittles hair and dices paper more silent than a ninja sneaking out of a poetry reading, but will carve hardwood and slice soft metals with the best of them. I've posted pics of an edge with a steel and angle suited for planing hundreds of feets of hardwood (if a planer could be made to hold a Spyderco Stretch ) only to have a viewer state the edge might be good for shaving, but not much else. Good for you, pal. I cut with my knives, so good for you and the horse you rode in on. Anyways, either viewing sharpness as contextual or reducing sharpness to just one of several factors in cutting ability lets the user decide on what sorts of specialized or hack-of-all-trades edges to apply to his or her knives.

D8XX ftw!

 

[QuietOned]

....but I also believe the dichotomy between sharpness and cutting ability resolves when sharpness is measured in the context of what's being cut and how it's being cut.

Totally true. Far to often people get caught up in the go for the gusto approach. Thin, High Polish to half an atom structure of some esoteric compound. Sharp gets the job done and I don't really care how you get there. If I'm going to be chopping fruit for a desert or slicing slivers of fish for sushi or whacking seatbelts or wet rope as fast as I can in an emergency or sharpening planner blades to slice end grain clean in curls I can almost see through. Using the edge for what you intend it is what matters. If I'm happy with it and it works don't tell me it won't work because it does, for me, for my purpose, and for the metal in my edge. There may be other ways to get there but for me I'm doing ok.

Of course, one can have a blisteringly keen edge which not only whittles hair and dices paper more silent than a ninja sneaking out of a poetry reading, ....

I chuckled at that but not knowing or having seen a ninja sneak out of poetry reading I had to think but don't ninja's like poetry? How about as quietly as a hung over sinner sneaking out of church to head to the bar for hair of the dog and to watch sports? I bet I could put a few ninja's to shame.

 

[thombrogan]

Thin, High Polish to half an atom structure of some esoteric compound.

Says the guy who bought a quarter of my boron carbide!

Sharp gets the job done and I don't really care how you get there. If I'm going to be chopping fruit for a desert or slicing slivers of fish for sushi or whacking seatbelts or wet rope as fast as I can in an emergency or sharpening planner blades to slice end grain clean in curls I can almost see through. Using the edge for what you intend it is what matters.

If that's all with the same knife, you must wear them down quickly! I remember you writing at knifeforums about not sharpening coarser than 220 or 320 for rescue knives or other knives cutting fibrous materials. And then there are the high-hardness knives and the evil biddings of Ken123 - I've got to give that some more tries soon after my new toy joy fades.

If I'm happy with it and it works don't tell me it won't work because it does, for me, for my purpose, and for the metal in my edge. There may be other ways to get there but for me I'm doing ok.

That's a common problem both face to face and on the interweb. It's really easy to mistake one's own opinions and methods for the immutable truth and state them with such conviction (I'm guilty of that!) instead of saying "another way you might achieve x is by doing y or z instead b" or "I've had good luck using blah blah blah and it's never failed me except for when it did."

I chuckled at that but not knowing or having seen a ninja sneak out of poetry reading I had to think but don't ninja's like poetry? How about as quietly as a hung over sinner sneaking out of church to head to the bar for hair of the dog and to watch sports? I bet I could put a few ninja's to shame.

Ninjas say they like poetry, but you never see them on open mic night.

 

[db]

I have had edges too thin, ouch did I really say that, too thick, to coarse, and too polished. I still will sharpen my knives these ways. Until you have tried different edges for your self and find what works best for the way and type of stuff you use a knife for. The best edge for you isn’t known no matter if it’s called sharp, stable, or has great cutting ability.

 

[thombrogan]

The best edge for you isn’t known no matter if it’s called sharp, stable, or has great cutting ability.

Bing bing bing!

<Balloons drop from the ceiling and chilled bottles of King Cobra are brought forth>

 

[WhitleyStu]

Yes, all the latest greatest sharpening devices and methods can leave the newbie feeling he doesn't have the ability to "keep up with the Jones" in the sharpening department. I can get that get that "Thin, High Polish to half an atom structure of some esoteric compound", but the box cutter edge does exist in my shop and it is the most used... But, I will never give up my strop!!!

 

[thombrogan]

But, I will never give up my strop!!!

Oh gnomes!

My three strops sit in a corner like that dude at the end of The Blair Witch Project, but occasionally are used.

Ever make a really coarse edge, deburr, and then strop? Feels like most factory edges.

 

[HoB]

I had a similar relevation about half a year ago. I was bend over my benchstones trying to achieve edges that would drop another few grams on my thread cutting test...till it suddenly occured to me, that I wouldn't be able to tell the difference between those edges if I didn't have the scale right next to me. So I began to wonder why the hell I really care whether the edge is able to cut thread at 25 or only at 30 g. I think that was the last time I used the scale for anything other than weighing my knives..... . I still think it is a great tool to test for edgeholding and ultimate sharpeness of different steels....but really by now I know how I expect a blade to cut. That is really all I need. The exhileration of the hunt for ultimate sharpness is pretty much gone. Not to mention that geometry changes have only a fairly indirect influence on thread cutting.

But I guess, it is human nature to push everything to the limit before we feel content to say: Been there, done that.

 

[HoB]

Ever make a really coarse edge, deburr, and then strop? Feels like most factory edges.

Yup, they are surprisingly efficient, especially on something like paper towels. The strop is usually my first go to for edge maintainance. When I am too lazy to pull out the stones.

 

[cerulean]

My three strops sit in a corner like that dude at the end of The Blair Witch Project

LMAO! :thumbup:

 

[hardheart]

Well, I went from never going past shaving sharp with the medium stone on a Lansky set at the 25 degree slot to setting reliefs at ~10 degrees and polishing the microbevel consistently. But, this also came with the switch to carrying a multitool constantly with a serrated blade and wood saw. I kinda find that all my plain edge cutting tasks are easier with a thinner geometry (wow), no matter the edge finish. Therefore, I polish and then can just let the edge degrade a bit before sharpening again (well, I of course almost never let it get that far nowadays) I also avoid the super steels for the most part. If it's thin enough to cut well, then it'll definitely take damage when I do something stupid, so steels in the area of AUS8 dent rather than chip and get screaming sharp without disintegrating my rotator cuff from work on the stones.

 

[thombrogan]

Good points, Hardheart.

Sometimes, though, the 'supersteels' are easier to sharpen than AUS-8 and Rostfrei/Inox. Getting them thinned out from their factory state will take its toll, though.

 

[Larrin]

You also have to remember that coarser edges hold an edge better in slicing, up to a point.

 

[sodak]

I'm still not sure what the hell you said. But it sounded purty!!!! I won't descend into redneck humor for a while, I need all the character references I can get!

One thing I've noticed, though, is some of the sharpest factory edges from Spyderco on their ZDP 189 knives will shave my armhair without touching skin, yet when I apply the Murray Carter 3 finger test, my fingers slide right down the edge with no danger of being cut.

Interesting. I'm going back to the fridge for more beer now....

 

[thombrogan]

One thing I've noticed, though, is some of the sharpest factory edges from Spyderco on their ZDP 189 knives will shave my armhair without touching skin, yet when I apply the Murray Carter 3 finger test, my fingers slide right down the edge with no danger of being cut.

Same here. Edges that will split armhair still on one's arm will feel glassy under my fingers. I have a suspicion that most factory edges are made with a belt grinder and a buffer, but most of mine aren't. Conclusion = I'm a lousy sharpener, but never share info with the edges.

 

[thombrogan]

You also have to remember that coarser edges hold an edge better in slicing, up to a point.

I'm doing that. Wear resistance plays a large role in that, too (finally! A use for wear-resistance!). It seems that high-volume/large-carbide steels do well either with thick, polished edges or thin, toothy edges while low-volume/small-carbide steels (AEB-L, anyone?) seem to do well either with thick, toothy edges or thin, polished edges. Most of the time.

 

[db]

I&#8216;m not really sure carbide size and volume really has much effect on thick, thin, polished, or coarse edges, unless your edge is a good deal under 10 degrees per side, and I&#8217;m not even sure about that. I believe very few are that thin on pocket knives like we all use every day. There has been a lot written about carbide volume and size and theory about it but you know what they say about theory and then there is..

 

[thombrogan]

I believe very few are that thin on pocket knives like we all use every day.

That's where the 8" wet grinder comes in - to get the edge very very thin. Then the D8XX removes as much of the hollow grind as possible and leaves the edge thinner.

 

[db]

That's where the 8" wet grinder comes in - to get the edge very very thin. Then the D8XX removes as much of the hollow grind as possible and leaves the edge thinner.

Thom you use those for thinning the edge grind, or the blade grind?

 

[thombrogan]

The wet-grinder thins the blade grind and takes the edge grind with it. The new edge gets ground in and polished either by hand or with a sharpening jig (EdgePro Apex w/all the trimmings).